1. Field of the Invention
The present invention relates to a technique for providing a corrugated rectangular waveguide or feedhorn and, more particularly, to a technique for providing a corrugated rectangular guide where the corrugated rectangular waveguide or horn is fabricated by forming, preferably by numerical machining, grooves of a predetermined depth and cross-section in a line into four electrically conductive plates and then arranging the plates to provide a hollow corrugated rectangular waveguide or horn where the edges of the grooves in each plate essentially meet the edges of the grooves in an adjacent plate.
2. Description of the Prior Art
Corrugated waveguide and horn radiators have been used for a wide range of applications in microwave antennas because of their favorable electrical properties. For the most part these corrugated waveguide and horns have been of a circular or conical configuration because it is easier to form the grooves or corrugations with such cross-section. Rectangular waveguides or horns, however, are preferred for certain applications.
Rectangular corrugated flexible waveguides have been manufactured from a smooth-wall metal tube which is corrugated in a predetermined manner to form the rectangular cross-section. In this regard see, for example, U.S. Pat. Nos. 3,974,467 issued to S. Tobita et al on Aug. 10, 1976 and 4,047,133 issued to M. Merle on Sept. 6, 1977.
Various techniques have been used to provide the corrugations within a horn or waveguide. For example, as disclosed in U.S. Pat. No. 3,949,406 issued to M. Yvard on Apr. 6, 1976 a horn comprises an outside sheet metal support on the inside of which is installed, one beside another, a great number of rings having a shape such that two adjacent rings form a corrugation. Such technique could also be applied to a rectangular guide or horn. A second technique is shown in U.S. Pat. No. 4,255,753 issued to E. Lovick, Jr. on Mar. 10, 1981 where a continuous wire coil is disposed on the inside of a metal support of a circular or rectangular cross-section.
As disclosed in U.S. Pat. No. 3,618,106 issued to G. H. Bryant on Nov. 2, 1971 which relates to antenna feed systems comprising corrugated waveguides or horns of square or rectangular cross-section, it has been found that undesirable modes which have the effect, among other things, of limiting bandwidth are set up in the waveguide or horn due to the varying depths of the grooves at the corners of the square or rectangular guide. Bryant solves this problem by inserting corner pieces in each corner of each corrugation, which method is impractical and inaccurate for production purposes.
The problem remaining in the prior art is to provide a technique for providing rectangular corrugated waveguide or horns which eliminate the varying corrugation depth at the corner and is adaptable for mass production purposes.